Im working on a trane gas furance about 15 years old, xL-90 model and serial I dont know right off hand. Wont light all the time. been locking it self out Friends of mine reset the power to it, and it came on for them and when I got there it was working fine

Hot surface ignitor replaced last winter and is still good, unit tries and lights but ignition board either doesnt send 24v to gas valve or gas valve sticking

i mainly work on commerical units so i was wondering if the residental trane's have a lot of gas valve problems or ignition module board problems

im going over to look at it soon because it stop working again, and comments or suggestion would be great thanks